NATO membership was long sought by President Yushchenko, who was voted out of office in a January election, and was vigorously opposed by Russia, who was loathe to see a traditional ally, and one with such a long, important border, join the rival alliance.

The move may forestall the confrontation over the Crimean port of Sevastopol, the seat of Russia’s Black Sea fleet for centuries and still rented by the Russian navy. If Ukraine was to join NATO, the former government made no secret of its intentions to oust the Russian from Sevastopol and potentially hand the port over to the alliance as a new NATO base in the region.